1. Field of the Invention
The present invention relates to a color copying machine and more precisely relates to a color separating device forming part of the copying machine.
2. Description of Related Art
In a conventional color copier, image data of an object are separated into three colors of R (Red, 620 nm), G (Green, 525 nm), and B (Blue, 450 nm) to successively form latent images on a photoconductive drum. These latent images are developed with yellow, magenta, and cyanine and are superimposed to produce a color copy.
FIG. 8 shows a copying system of a known color copier. In FIG. 8, a scanning unit S having therein an illuminating light source 12 and scanning mirrors 13 and 14 is provided below a transparent glass plate 11 on which an object (document) 0 is located. The scanning unit S having the illuminating light source 12 and the scanning mirrors 13, 14 incorporated therein is scanned from a position shown by a solid line S to a position shown by an imaginary line S'(12', 13' 14'). The light which is emitted from the light source 12 (12') is reflected by the document 0 and then by the mirrors 13 and 14 and is transmitted onto a photoconductive drum 17 through a wavelength selecting filter (color separating mechanism) 15, an imaging optical system 16, and immovable mirrors M.sub.1, M.sub.2, M.sub.3. On the circumference of the photoconductive drum 17 are provided various known color copying elements, such as a charger 18, a developing unit assembly 19 having developing units (19a for yellow, 19b for magenta, 19c for cyanine and 19d for black) corresponding to the respective selected wavelengths, and a transfer unit 20, etc. In FIG. 8, 21 designates a paper on which the image is to be copied, and 22 a paper feeder therefor.
In the known arrangement as shown in FIG. 8, the color separating mechanism 15 which is located in front of the imaging optical system 16 successively inserts color filters of the three colors (R, G and B) in the optical path of the imaging optical system to effect the color separation. Alternatively, it is also known to arrange, between the light source 12 and the document 0, a color separating mechanism in which the color filters R, G and B are selectively inserted into the optical path to carry out color separation. When the scanning unit S is scanned for respective colors, image data (i.e. of the latent image) which are separated into three colors R, G and B are formed on the photoconductive drum 17.
In the developing unit assembly 19, the developing unit (yellow) 19a is used for the latent image which is formed by the color filter B, the developing unit 19b (magenta) for the latent image which is formed by the color filter G, and the developing unit 19c (cyanine) for the latent image which is formed by the color filter R. The latent images developed on the photoconductive drum 17 are superimposed on the same paper 21 to obtain a desired color copy.
In the color separating mechanism 15, there is a need for quickly and certainly changing the three or four) color filters G, B and R (and M for monochrome, if necessary) within a small space.
For instance, Japanese Examined Patent Publication (Kokoku) No. 55-30232 disclosed a concentric arrangement of color filters which radially extend about a rotational shaft, so that when the rotational shaft rotates, the color filters are selectively introduced into the optical path. However, the arrangement disclosed in this publication needs a relatively large space for accommodating the rotational movement of the color filters.